Add option to pause background movement animation

[laxsjo]

While the moving background visible on all pages (see example below) does look very cool and sexy, and I definitely think you should keep it, it can be quite distracting for certain kinds of users (including me), and is therefore an important accessibility feature.

It would be nice if there was an option to pause this animation. It would of course also be important that the state of this button (or however it is implemented) is remembered between page loads.

Here is an example of how it looks today:

[laxsjo]

I could definitely implement a solution myself if that is something you are open to. The codebase doesn't look that complicated. :)

The only question would be where to place the JavaScript for this. As it would require a non-trivial amount of code, inlining it in a script tag feels cumbersome, especially considering that this code would be duplicated across all routes then. Could this warrant a new separate JS file?